Organ size is an important characteristic of plant morphology. Under the same growth conditions, there is little difference in organ sizes among individuals having the same genotype and within the same species. For different species, the size of seeds and other organs vary greatly, while the individuals belonging to one species have relatively uniform sizes of seeds and other organs of similar size. These facts show that organ size in plants is strictly under genetic control. Meanwhile, the morphogenesis of a plant organ is influenced intensively by the external environment (including factors such as: light, temperature and nutrition). Thus, the mechanism on controlling a plant organ size is very complicated, as is the internal mechanism of a plant which precisely controls the predetermined size of an organ when finally grown. Organ size in a plant is an important yield trait. Thus, an investigation on the sizes of seeds or other organs in a plant will provide a theoretical basis and some novel genetic sources for possible genetic modifications which may be used in developing transgenic high-yield crops.
Plant organ sizes may greatly vary depending on the species. Besides the restrictions of natural conditions, artificial selection has a significant effect in plant organ size. Although the mechanism of organ size self-controlling in a plant is still not clear, there are at least two known potential factors that dominate the organ sizes in a plant, i.e. cell number and cell size. Generally, the size of the same organ in a different species is determined by the cell number therein. However, changing cell number or cell size singly may not always lead to the change of organ size. This is because the variation of one factor may be compensated by other factors. For example, a decrease in cell number of an organ may not lead to a smaller plant organ, because the plant may make up for the decrease of cell number by increasing total cell volume so that the whole organ maintains the same size. Such a coordination mechanism in cell growth suggests an endogenous regulation in the plant itself. Some recent studies have found some critical genes in gene pathways that function to control organ sizes by affecting cell number, cell size or both.